Will learning Titanium Appcelerator improve my understanding of NodeJS?
No. Titanium is an API around the native iOs, Android, etc libraries for building mobile apps. Most casual users will never delve into the internals of whatever js engine Titanium uses under the covers.
You will learn more about node.js by building node.js apps. If you want to learn about v8, you can always download the source. Same for node.js.